I have been a long time GalCiv customer and love the game greatly.  I do not get to play it as often as I would like but anytime I have a few free moments I play a few turns. 

I recently bought (last week) Sins of a Solar Empire via impulse.  I know I am almost a 1 year late in coming to the party but when it came out I was still deep into GalCiv love and I had a hard time dealing with the fact that it was not enough like Homeworld.

But all of that is water under the bridge.  I buying SoaSE it caused me to wonder.  Just what is the life cycle of a computer game anyway?  I know they are getting ready to release a small and cheap enhancement but besides that how does shelf live and revenue compare between games sold at the store vs through something like Impulse?